Who was making ignition insulator on valve cover

I don't know who's photo this is but the round ones on the driver's side is what I'm talking about.

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On my car the driver's side were not painted.



The pass side were painted.

Kind of makes me think that the factory did this to assist with plug wire install, round on the wires go to driver's side.
That would be mine. It's a 66 with the original covers and insulators.